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Idiomatic Kotlin patterns, best practices, and conventions for building robust, efficient, and maintainable Kotlin applications with coroutines, null safety, and DSL builders.
Passed 22 of 22 test cases with the skill, and 20 of 22 without it.
2 fixed20 passed either way0 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 2 test cases the skill fixed. Same model, same prompt, with and without the skill.
In a Kotlin backend endpoint, we need to load dashboard widgets (user info, notifications, recommendations). If notifications or recommendations fail with an exception, we want to catch it and return empty lists for those widgets rather than failing the entire request. How should coroutine parent-child failure propagation be configured?
| Checked | Without skill | With skill |
|---|---|---|
| Configures parent scope so failure in one child task does not automatically cancel sibling tasks. | Passed | Passed |
| Rethrows `CancellationException` explicitly when catching exceptions inside child jobs. | Missed | Passed |
The instructions your model reads when the skill loads.
Idiomatic Kotlin patterns and best practices for building robust, efficient, and maintainable applications.
This skill enforces idiomatic Kotlin conventions across seven key areas: null safety using the type system and safe-call operators, immutability via val and copy() on data classes, sealed classes and interfaces for exhaustive type hierarchies, structured concurrency with coroutines and Flow, extension functions for adding behaviour without inheritance, type-safe DSL builders using @DslMarker and lambda receivers, and Gradle Kotlin DSL for build configuration.
Null safety with Elvis operator:
fun getUserEmail(userId: String): String {
val user = userRepository.findById(userId)
return user?.email ?: "[email protected]"
}
Sealed class for exhaustive results:
sealed class Result<out T> {
data class Success<T>(val data: T) : Result<T>()
data class Failure(val error: AppError) : Result<Nothing>()
data object Loading : Result<Nothing>()
}
Structured concurrency with async/await:
suspend fun fetchUserWithPosts(userId: String): UserProfile =
coroutineScope {
val user = async { userService.getUser(userId) }
test cases passed, vs 20 / 22 without
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